Ionic liquids are liquids composed of ions that are fluid at or below about 100° C. Ionic liquids exhibit negligible vapor pressure, and with increasing regulatory pressure to limit the use of traditional industrial solvents due to environmental considerations such as volatile emissions and aquifer and drinking water contamination, much research has been devoted to designing ionic liquids that could function as replacements for conventional solvents.
Ionic liquids typically consist of a salt of an organic cation such as the N-alkylpyridinium, 1,3-dialkylimidazolium, tetraalkylammonium, tetraalkylphosphonium or trialkylsulfonium cation. U.S. Pat. No. 7,157,588 describes, for example, ionic liquids based on N-substituted pyrrolidones, which have a pendant ammonium cation that is spaced from the pyrrolidone ring by a variable length linker. A need remains, however, for other ionic liquids that may be designed for use in selected applications, particularly those that may be prepared at least in part from renewable resources.